Referring to FIG. 1, a conventional fan structure 10 was manufactured by method of injection molding with a forming mold (not shown in Fig). The fan structure 10 comprises a base 11, a hub 12 disposed on the base 11, a casing 13 and a plurality of fan blades 14 be in communication with the casing 13 and the base 11. In order to provide a high static pressure capability, the number of the fan blades 14 will be increased so that the spacing D between each of the fan blades 14 will be decreased thereby causing processing difficulty. Moreover, the mentioned forming mold must be fabricated by methods of wire-cut or electrical discharge to lead higher cost. Besides, in the manufacturing process of the fan structure 10, shrinking the spacing D may cause low mechanical strength and long fabricating time by using a cutting tool having small diameter instead of a cutting tool having large diameter. Tool life of the cutting tool having small diameter are shorter than one having large diameter through repetitive processing.